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United States Patent |
5,354,787
|
Shimoda
,   et al.
|
October 11, 1994
|
Soil-stabilizing agent and a method for soil-stabilizing treatment
Abstract
It is an object of the present invention to provide a soil-stabilizing
agent with less emission of dust, good reactivity, good behavior at mixing
and good dispersibility and a method for soil stabilizing treatment
capable of restraining the emission of dust in the procedure of sprinkling
and mixing of the soil-stabilizing agent to soil.
The soil-stabilizing agent according to the present invention comprises a
mixture of a material mainly composed of quick lime and/or calcined
dolomite and fibrillatable polytetrafluoroethylene resin.
And the method for soil-stabilizing treatment according to the present
invention comprises the following steps; adding a mixture of a material
mainly composed of quick lime and/or calcined dolomite and fibrillatable
polytetrafluoroethylene resin to soil, and mixing them under the hydration
heat generated by the reaction between the quick lime and/or calcined
dolomite with moisture in the soil to form hydrated material.
When PTFE is in partially fibrillated state, emission of dust while
sprinkling (primary dust) from the soil-stabilizing agent will be
restrained as the particles of quick lime and/or calcined dolomite are
enclosed in a cobweb-like net of the partially fibrillated PTFE, and
emission of dust while mixing (secondary dust) is further restrained by a
cobweb-like net of PTFE fibrillated further by mixing under hydration heat
generated by the reaction of quick lime and/or calcined dolomite with
moisture in the soil.
Inventors:
|
Shimoda; Tetsuya (Hachioji, JP);
Ishikawa; Katuaki (Yokohama, JP);
Urano; Teruo (Sano, JP);
Miyaji; Hiroshi (Utsunomiya, JP);
Ogura; Masatsune (Ichikawa, JP)
|
Assignee:
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Nippon Hodo Co., Ltd. (Tokyo, JP);
Murakashi Lime Industry Co., Ltd. (Tochigi, JP);
Du Pont-Mitsui Fluorochemicals Co., Ltd. (Tokyo, JP)
|
Appl. No.:
|
013050 |
Filed:
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February 4, 1993 |
Foreign Application Priority Data
| Oct 19, 1987[JP] | 62-261838 |
Current U.S. Class: |
523/132; 524/424; 524/427; 524/433; 524/546 |
Intern'l Class: |
C09K 017/00 |
Field of Search: |
523/132
524/424,427,433,546
|
References Cited
U.S. Patent Documents
3838092 | Sep., 1974 | Vogt et al. | 524/546.
|
4134862 | Jan., 1979 | Eden et al. | 523/132.
|
Foreign Patent Documents |
60-191084 | Sep., 1985 | JP.
| |
Other References
Kirk-Othmer "Encyclopedia of Chemical Technology" 2nd Edition, vol. 9,
812-814.
Raiil et al., "Studies of the Morphology of Emulsion-Grade
Polytetrafluorethylene." Journal of Polymer Science: Part A-2, vo.. 10
(1972), 1337-1349.
Chem. Abstracts vol. 104, 1986, 50365j, Urano Teruo; Miyaji, Hiroshi "Leach
Proof Slaked Lime Fertilizers" p. 474.
Grant & Hackh's Chem. Dictionary, 1987, p. 234, fibril.
Webster's II New Riverside Dictionary, 1984, p. 474, fibril, fibrillate,
fibrillation.
Japan Kokai, Full translation, English 60-191084.
|
Primary Examiner: Michl; Paul R.
Assistant Examiner: Guarriello; John J.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Parent Case Text
This is a division of application Ser. No. 07/728,030, now U.S. Pat. No.
5,210,112 filed Jul. 8, 1991, which is a continuation of Ser. No.
07/530,435, filed Jun. 1, 1990, now abandoned, which is a continuation of
Ser. No. 259,374, now abandoned, filed Oct. 18, 1988.
Claims
We claim:
1. A method of stabilizing soil and controlling associated dust by applying
to soil in need of soil stabilization a soil stabilizing effective amount
of an agent comprising:
a) not less than 90 wt % of quick lime and/or calcined dolomite;
b) 0-10 wt % of slaked lime and/or hydrated calcined dolomite; and
c) partially fibrillated polytetrafluoroethylene resin in an amount of
0.01-1.0 wt % of the material mainly composed of quick lime and/or
calcined dolomite which has been added for dust control.
2. A method of stabilizing soil according to claim 1, wherein the quick
lime and/or calcined dolomite is in powdery or fine granular state.
3. A method of stabilizing soil according to claim 1, wherein the quick
lime is a soft-burnt lime or a quick lime calcined in the presence of
sodium chloride.
Description
FIELD OF THE INVENTION
The present invention relates to a soil-stabilizing agent and a method for
soil stabilizing treatment intended to prevent the emission of dust while
sprinkling or mixing of CaO-containing soil-stabilizing agent such as
quick lime or calcined dolomite, and to improve the reactivity, the
behavior at mixing and the dispersibility of the soil stabilizing agent.
DESCRIPTION OF THE PRIOR ART
In Japan, weak ground composed of clayey soil such as a clayey soil mainly
consisted of volcanic ashes as represented by Kanto-loam stratum is widely
distributed.
These soils are difficult to handle from the view point of soil technology,
and some measures are necessary to be taken to prevent the sinking of road
and buildings after construction.
Measures to treat the weak ground has developed remarkably in Japan since
1960's with the development of materials and treating machines in the soil
improvement works.
Although lime itself is not a main material now, the effect of soil
improvement is essentially based on lime.
As the weak ground has a character of high moisture content in general,
CaO-containing material such as quick lime (CaO) or calcined dolomite
(CaO+MgO) is effective for improvement of the weak ground. The mechanism
of soil improvement with CaO-containing material is shown in the following
Table 1, representing the CaO-containing material by quick lime.
TABLE 1
______________________________________
Quick lime is added to weak ground.
##STR1##
##STR2##
##STR3##
______________________________________
As the weak ground is composed of soil particles and pore water, rapid
dehydration of the pore water by slaking reaction of the quick lime can
improve the plasticity of the soil. The decrease in moisture content is
promoted with the evaporation of water by generated heat, with the
compression by expansion of the lime and with the adsorption of water by
slaked lime powder formed. The slaked lime powder formed is ionized to
Ca.sup.2+ and OH.sup.-, and the Ca.sup.2+ makes an ion exchange reaction
with other cations on the surface of the clayey soil to change the state
of electric charge on the surface of soil particles to facilitate the
coagulation of the soil particles. Then, with the lapse of time, the lime
converts to a new material by pozzolan reaction with silica and alumina
composing the clayey soil to solidify under an alkaline atmosphere.
As the soil stabilizing agent, the quick lime or the calcined dolomite is
used in a form of powder or granule with a size of from dozens millimeter
to under several millimeter. The amount to be used is usually about 3-20
percent of dry weight of the soil, though it is variable depending upon
the kind of the soil and moisture content of the soil. Some additives can
be used to promote the reaction of quick lime and/or calcined dolomite
with the soil. As the additive, gypsum, slag cement, cement, clay powder,
fine powder of iron oxide and fly ash etc. can be used.
There are many kinds of methods such as the central mixing method or field
mixing method at the soil-stabilizing treatment, and the quick lime pile
method or the deep layer mixing method at the ground-improving treatment.
Although the "ground-improving" and the "soil-stabilizing" have essentially
same meaning, stabilizing treatment in a shallow layer is called as
soil-stabilizing or soil-stabilizing treatment, and stabilizing treatment
in a deep layer is called as ground-improvement in general. However, in
the present invention, both cases are included.
The decrease in moisture content is very effective for the soil stabilizing
treatment in clayey soil with high moisture content. But the decrease in
moisture content is not easy in many cases.
As mentioned above, when quick lime or the like is mixed with clayey soil
with high moisture content, it reacts with moisture contained in the
clayey soil immediately and makes mechanical and chemical change of the
soil such as dehydration by formation of slaked lime (calcium hydroxide).
It results in the decrease in moisture content, the decrease in plasticity
index, the improvement in compaction property and the improvement in
workability.
Shortening of the treatment time which can be achieved by rapid progress of
the dehydration by the above-mentioned function of the quick lime is the
most important merit of the quick lime type materials as the
soil-stabilizing agent.
On the other hand, the dust problem is one of the demerit of the quick lime
type soil-stabilizing agent.
A lot of fine dust of quick lime or its reaction product is emitted while
sprinkling or mixing of quick lime. It causes many problems such as the
contamination of environment, the health hazard to workers and the
contamination of treating machines, and now people are worrying about
these problems.
Although powdery or fine granular quick lime has better dispersibility and
easiness of mixing and consequently it has better reactivity than lumpy or
large granular quick lime, it is practically difficult to use it for
methods other than the central mixing method because of the emission of
dust at the time of sprinkling. So in the field mixing method, expensive
lumpy or large granular quick lime is used to prevent the emission of dust
while sprinkling.
However, even when the lumpy or large granular quick lime is used in the
field mixing method, the quick lime tends to concentrate locally due to
uneven mixing at primary mixing. In much the same way, a very large
quantity of the quick lime is added intensively in a pile shape in the
quick lime pile method. In these cases, contact of the quick lime with
soil and absorption of moisture in the soil becomes insufficient, and a
large mass of unreacted quick lime and slaked lime is apt to be formed
locally.
Consequently, the emission of dust occurs actually not only while
sprinkling but also while secondary mixing.
So, when the emission of dust should be avoided strictly such as the case
of construction works in urban districts, alternative method using humid
slaked lime or slaked lime slurry should be adopted at the sacrifice of
the dehydration effect of the quick lime.
By the way, it has been known that a kind of polytetrafluoroethylene
(referred as PTFE hereinafter) forms ultra fine cobweb-like fibrils under
compression-shear at an appropriate temperature.
In Japanese Patent Publication Tokko Sho 52-32877 (corresponding to U.S.
Pat. No. 3,838,064), it has been disclosed a method for dust-control
treatment wherein an effective quantity of fibrillatable PTFE powder is
added to dusty powder under compression-shear by agitation at a
temperature of about 20 .degree. to 200.degree. C.
Fibrillation of PTFE is said to start at about 20.degree. C. However, in
practical industrial purposes, it is desirable to give compression-shear
at a temperature above 50.degree. C., preferably above 80.degree. C.
Accordingly, when the temperature of the dusty powder is low, it is
required to heat it to a temperature above 80.degree. C., requiring enough
heat energy and a heating apparatus.
In Japanese Patent Provisional Publication Tokkai Sho 60-191084, it has
been proposed a manufacturing method of slaked lime fertilizer with
anti-flux property whose particles are covered and coagulated with
cobweb-like net wherein quick lime is added with fibrillatable PTFE powder
dispersed in a certain quantity of water necessary to hydrate the quick
lime and given a compression-shear by agitation at an elevated temperature
caused by an exothermic hydration reaction of the quick lime and the
water.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a soil-stabilizing
agent with less emission of dust, good reactivity, good behavior at mixing
and good dispersibility and a method for soil stabilizing treatment
capable of restraining the emission of dust in the procedure of sprinkling
and mixing of the soil-stabilizing agent to soil.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The soil-stabilizing agent according to the present invention comprises a
mixture of a material mainly composed of quick lime and/or calcined
dolomite and fibrillatable polytetrafluoroethylene resin.
And the method for soil-stabilizing treatment according to the present
invention comprises the following steps; adding a mixture of a material
mainly composed of quick lime and/or calcined dolomite and fibrillatable
polytetrafluoroethylene resin to soil, and mixing them under the hydration
heat generated by the reaction between the quick lime and/or calcined
dolomite with moisture in the soil to form hydrated material.
It should be understood that the soil-stabilizing treatment in the present
invention includes not only the stabilizing treatment of shallow layer of
the ground in narrow sense, but also the ground-improvement treatment in
deep layer of the ground. It also should be understood that the weak
ground means not only so-called weak ground, but also sludge-like ground.
Representative fibrillatable PTFE can be obtained by a method disclosed by
Barry in U.S. Pat. No. 2,559,752 wherein tetrafluoroethylene monomer is
polymerized in an aqueous medium containing fluorocarbon surfactant.
PTFE particle obtained by the above mentioned method is a colloidal
particle having a particle size in a range of 0.05-0.5 micron and a
surface area above 10 m.sup.2 /g. It can be obtained in a form of an
aqueous dispersion or in a form of powder coagulated from said aqueous
dispersion and either of which can be used in the present invention.
In the soil-stabilizing agent according to the present invention, PTFE is
desirable to be in partially fibrillated state. The partially fibrillated
state is explained as follows.
As mentioned above, particles of PTFE are fibrillated under
compression-shear at an appropriate temperature. If an excess external
force is given to the fibrils, aspect ratio of the fibril (length/cross
sectional area of the fibril) becomes so large to the extent that the
diameter of fibrils becomes too small to be unable to enclose dusty powder
effectively by the fibrils.
The partially fibrillated state (it may be also expressed as
half-fibrillated state) means a state wherein a part of PTEF particles is
fibrillated or a state wherein the aspect ratio of fibril is small. From
the viewpoint of phenomena, it means a state wherein PTFE is capable of
further fibrillation and enclosing dusty powder again by further addition
of compression/shear under heating. Said partially fibrillated state can
be achieved by using rather much amount of PTFE or with rather weak
mixing.
The soil-stabilizing agent wherein PTFE is in partially fibrillated state
can be prepared by slightly stirring a mixture of quick lime and/or
calcined dolomite and PTFE at a high temperature. The high temperature can
be attained by the remaining heat after calcination of lime stone or
dolomite or by the hydration heat generated by addition of aqueous
dispersion of PTFE to quick lime and/or calcined dolomite, which means
that no external heat is required.
When PTFE in the soil stabilizing agent is in partially fibrillated state,
emission of dust while sprinkling (primary dust) from the soil-stabilizing
agent is restrained as the particles of quick lime and/or calcined
dolomite are enclosed in the cobweb-like net of the partially fibrillated
PTFE, and emission of dust while mixing (secondary dust) is further
restrained by cobweb-like net of PTFE fibrillated further by mixing under
hydration heat generated by the reaction of quick lime and/or calcined
dolomite with moisture in the soil.
Suitable amount of PTFE is 0.01-1.0 weight percent, preferably 0.03-0.5
weight percent of a material mainly composed of quick lime and/or calcined
dolomite. If the amount is too small, the effect of dust control is poor,
and if the amount is too much, it is not desirable from the viewpoint of
dispersibility and cost.
The material mainly composed of quick lime and/or calcined dolomite is
desirable to be powdery or fine granular state from the viewpoint of the
easiness at mixing, the dispersibility and the reactivity.
The quick lime and/or the calcined dolomite is desirable to be calcined as
weakly as possible, because its hydration reaction begins all at once, and
generated heat can be used effectively.
For example, it is desirable to use a quick lime of which hydration
activity value expressed by a titration volume of 4N-HCl for 50 g quick
lime with a particle size of 2 millimeter sieve pass is more than 300
milliliter within 10 minutes.
So-called salt-calcined quick lime obtained by calcination of 1 ton of
limestone in the presence of 2-5 kg of sodium chloride is preferable too
from the viewpoint of effective utilization of reaction heat, as it is
more porous than usual quick lime and has a good moisture absorbing
ability to complete the hydration reaction within a short period of time.
In addition to the material mainly composed of quick lime and/or calcined
dolomite and fibrillatable PTFE, the soil-stabilizing agent of the present
invention may contain some additives such as gypsum, slag cement, cement,
clay powder, fine iron oxide and fly ash and so on.
When the soil-stabilizing agent of the present invention is added to soil,
heat of hydration is generated as the moisture in the soil is absorbed in
the soil-stabilizing agent and reacts with the quick lime and/or the
calcined dolomite in the soil-stabilizing agent to form hydrated
compounds. If soil and the soil-stabilizing agent is mixed and stirred
with good timing based on a data obtained by an experimental measurement
of slaking rate and temperature increase, dusty powder is enclosed by
cobweb-like net of further fibrillated PTFE, and the secondary emission of
dust can be restrained.
At that time, if the quick lime and/or the calcined dolomite is in powdery
or fine granular state, because of the behavior at mixing, the
dispersibility and the reactivity is excellent, the heat of hydration
generates quickly to reach the highest temperature in a short period of
time with little deviation of the time to make it easy to catch the good
timing of mixing and fibrillation of PTFE.
In this manner, the dust problems in the soil-stabilizing treatment such as
the primary emission of dust at the sprinkling and the secondary emission
of dust at the mixing can be restrained to make it possible to use powdery
or fine granular quick lime and/or calcined dolomite having good
reactivity and fundamentally suitable property for the soil-stabilizing
treatment.
EXAMPLE 1
Preparation of a soil-stabilizing agent
1,000 kg of quick lime pulverized by a crusher to a particle size of 5
millimeter sieve pass was charged in a 1,500 liters mortar mixer and 23.0
Kg of 1.96 weight percent aqueous dispersion of fibrillatable PTFE (made
by diluting the aqueous dispersion of Teflon K20-J [trade name]:
corresponding to 0.045 weight percent of PTFE per the quick lime) were
added gradually under stirring of 27 rpm for one minute.
While stirring, a part of the quick lime was converted to slaked lime due
to the reaction with water in the aqueous dispersion of PTFE accompanying
some heat generation and the quick lime powder became dust free itself.
Thus obtained composition was used as the soil-stabilizing agent.
Dust-control test
5 kg of the above mentioned soil-stabilizing agent was filled into a hole
with a diameter of 15 cm and a depth of 20 cm dug in a Kanto loam soil
road with a moisture content of 40-50 weight percent. A thermometer was
set in a depth of 10 cm at the center of the hole.
As the thermometer showed 80.degree. C. after 4 hours and 70.degree. C.
after 5 hours and swelling and powdering on the surface of the lime was
observed by eyes, it was judged that the hydration reaction had finished.
Then lime powder within 1-2 cm depth from the surface was collected to a
vat by a scoop. The collected powder in the vat was not dusty after
stirring once or twice by the scoop.
Then the soil around the hole within a diameter of 40 centimeter and the
soil-stabilizing agent was mixed by a scoop.
Only a little emission of dust with negligible order was observed at the
beginning of the mixing.
Comparative Experiment
A pile with a diameter of 30 centimeter and a thickness of 2.5 meter
composed of quick lime with particle size of under 2 millimeter was set
into a silt ground with a moisture content of 80-120 weight percent by a
piling machine.
As the temperature in the depth of 50 cm at the center of the quick time
pile was 180.degree.-200.degree. C. at 30 minutes after the setting and
became 150.degree.-160.degree. C. at 1 hour after the setting, it was
concluded that slaking of the quick lime had finished. Soon after that, a
mixing operation was carried out using a uniaxial mixing machine with
propeller-shaped stirring blades capable of mixing within a range of 1
meter diameter with an average ascent or descent speed of 1.0 meter per
minute and a torque of 500-1000 ton-meter. Although the behavior at mixing
and the dispersibility of the lime was good, remarkable emission of dust
was observed.
Then another pile of quick lime was set in the same manner as mentioned
above. After 3 hours the quick lime became mud by hydration and adsorption
of moisture in the soil. Then they were mixed by the uniaxial mixing
machine. Although emission of dust restrained, the lime which became mud
state could not disperse in the silt soil uniformly, and the behavior at
mixing and the dispersibility was bad.
EXAMPLE 2
A pile was set in the same manner as mentioned in the Comparative
Experiment except for a soil-stabilizing agent prepared in the same manner
as mentioned in Example 1 (quick lime added by PTFE: particle size of
under 2 millimeter) was used for the pile and mixed by the uniaxial mixing
machine.
Although a little amount of dust was emitted at the beginning of the
mixing, the emission of dust was ceased after several times of rotation of
the stirring blades, and the behavior at mixing and the dispersibility was
good. It means that the mixing work can be carried out within a short
period of time after the setting of the pile with good behavior at mixing
and dispersibility and without a remarkable emission of dust.
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